When evaluating whether a given earth formation contains valuable materials, such as hydrocarbons, a core sample from the earth formation may be procured using a bottom-hole assembly (BHA) often referred to in the art as a “coring tool.” A coring tool generally includes a core bit, which may be a hollow earth-boring rotary drill bit having a longitudinal aperture extending through the center thereof. As a result, when the core bit drills through the formation, a generally cylindrical core sample is formed within the longitudinal aperture extending through the center of the core bit. A substantially non-rotating inner barrel is positioned longitudinally within an outer tubular member, commonly termed a “core barrel” of the coring tool above the core bit, and is configured and positioned to receive the generally cylindrical core sample therein as the core sample is formed by the core bit as the core bit drills into the earth formation and the coring tool lowers around the core sample.
Once the core bit has drilled a core sample of desirable length, a core catcher is used to fracture the core sample and separate the core sample from the formation near the core bit. The core catcher is typically a collet structure that allows the core sample to pass through the collet into the inner barrel of the coring tool, but that tightens around the core sample when the coring tool is pulled upward away from the bottom of the wellbore to prevent the core sample from backing out from the coring tool through the core catcher. In other words, when the coring tool is pulled upward away from the bottom of the wellbore, the core catcher grips the core sample and generates tensile forces within the core sample below the core catcher that fracture the core sample, allowing it to be retained within the inner barrel and returned to the surface for analysis.
Some formations comprise loose or unconsolidated formation material. For example, some formations may comprise unconsolidated sand. In such formations, a collet type core catcher may not retain all of the core sample within the inner barrel, as the loose formation material may simply fall out of the coring tool through the opening of the core catcher. Other configurations of core catchers have been developed in an effort to retain such unconsolidated formation material within the inner barrel of the coring tool. For example, flap catchers have been developed that include one or more flap members that move between a first open position and a second closed position after a core sample has been formed and received within the inner barrel. The flap catcher substantially covers the central opening in the core bit, which forms the core sample as the core bit drills the formation material around the core sample, and prevents or at least hinders unconsolidated material from falling out from the coring tool as the coring tool is returned to the surface for analysis of the core sample.